Tuesday, October 21, 2014

Michael Nave is a chestnut grower in California. He posts on on The Chestnut Forum. He is very generous with his knowledge.

Grams per nut -to- Nuts per pound

Some people think in terms of grams per nut, or grams per sample of three nuts (the typical number of nuts in a chestnut burr). Other people are more comfortable thinking in terms of nuts per pound.

The table shown above is a way to switch between grams/nut sample to nuts per pound. For example, the three nut sample in the top photo weighs 122 grams. If that is representative of all nuts in the population than one would expect between 10 and 12 nuts to the pound.

For a long time I was under the delusion that there was only one species of temperate, Western European oak: Quercus robur.

I was wrong.

Quercus robur is the oak of the deep, rich soils and protected coves of Western Europe...the cozy Western Europe of Thomas Hardy. Quecus petraea is the oak of the shallow soil, of windy exposed knobs and of stony, acidic soil. That would be the western Europe of the Bronte sisters and the Hounds of Baskerville.

===>This essay<=== explains how to determine if an oak specimen is Q. robur, Q. petraea or a nominal hybrid between the two.

Six specimens collected form my property. Roughly sorted, more robur like on bottom-right corner, more petraea like in upper-left corner.

Bottom right specimen: Petiole and auricles suggest pure Q. robur

Top-middle specimen, longish (9% of leaf length) petiole and lack of auricles suggests that this specimen is not pure Q. robur.

The reason I hedge my bets and say "...not pure Q. robur" is that these specimens were from seeds collected in Michigan and potential pollen parents also include Q. alba, Q. bicolor, Q. macrocarpa and Q. muhlenburgii as well as Q. petraea from the originating source in Europe.

Tuesday, October 7, 2014

I live in Michigan and it is illegal to import chestnut trees or scionwood from states known to harbor Asian Chestnut Gall Wasps.

Light green is the natural range of the American Chestnut before the Chestnut blight showed up.

A list of states with documented populations of ACGW include:

Georgia,

Alabama,

North Carolina

Virginia

Maryland

Pennsylvania

Maryland

Kentucky

Tennessee

Ohio

Connecticu

Ontario, Canada

Controls

The first line of defense is to not import it. If in doubt, don't.

The second line of defense is sanitation. If it looks like it has galls, cut and burn the infected material. Call your extension agent if you are in a state that is not documented as a ACGW positive state for positive identification.

The third line of defense is a cluster of parasitic wasps: Torymus sinensis, T. tubicola, Megastigmus

Native parasitic wasps are being identified as well. These native species have not been effective in suppressing populations because they are not synchronized with peak ACGW vulnerability. This situation is similar to what is seen with the Emerald Ash Borer. Given time it is likely that a genetic shift will occur so native species can exploit this bonanza of potential hosts.

One thing that growers can do is to plant prime nectar sources in or near their trees to hit the end-of-May to middle-of-July time window so the parasitic wasps can maximize their time spent hunting the target, ACGW. More research needs to be done to identify prime nectar sources. Potential plants include Mints, common white clover, sweet alyssum, Aegopodium podagraria, and possibly Eupatoriumperfoliatum if you can find an early blooming race. These nectar plants are suggestions.

Composites (Dandelion?) and Umbelliferae are highly regarded nectar sources but they may be more difficult to integrate them into your orchard management plan as easily as white clover and sweet alyssum. Beekeepers tell me that common garden raspberries and rhubarb attract vast swarms of native insects. The rhubarb is a bit early for our purposes but the raspberries fall within the early part of the sweet spot. No information is available regarding best cultivars although one would expect more berries to be correlated with more blossoms.

To reiterate, there may be relatively few native parasitic wasps that have populations peaks that coincide with when the ACGW is most vulnerable. Literature suggests that optimum feeding of parasitic wasps can increase their life span by a factor of three-to-five times. That increases the breeding efficiency of those races/species of wasps life cycles that do align with the ACGW, will hasten the speed of the genetic shift that will result in synchronization with the ACGW and by slowing down parasitic wasp mortality will increase the number of parasitic wasps per unit of land during periods of peak ACGW vulnerability.

Sunday, August 10, 2014

We have recently found that a type of kernel rot, not associated with a
mold or insect, is found in about 30% of the nuts from ‘Colossal’ trees
when those trees are pollinized by Chinese chestnut....we strongly suggest keep Chinese cultivars
from pollinizing ‘Colossal’. At this time we are not sure if this
affliction will show up in all European/Japanese hybrids and if all
Chinese chestnuts cause it. To be safe we suggest keeping
European/Japanese hybrid and Korean (Japanese) cultivars 500 to 1000
feet away from sources of Chinese chestnut.

Wednesday, August 6, 2014

Many species of fruit and nut trees tend to "alternate" bearing. A more precise term is "synchronized" bearing because the years of heavy bearing are not always on a two year cycles.

Not all individuals in a give species show synchronized bearing traits. That tells us that there must be some significant selection advantage to synchronized bearing in those species where most individuals do exhibit sychronized bearing.

Environmental factors that contribute to synchronized bearing

Specimens that have fully exploited the nutrients in their root zone tend to be more strongly synchronized. The specimen will set an enormous crop. The maturing crop sucks an enormous amount of both carbohydrates and nitrogen (protein) out of the tree. The summer buds "decide" to take the vegetative form based on the dearth of resources needed to ripen next years crop. Depending on the site and climate it may take several years before the tree "triggers" another mammoth crop.

Commercial fruit growers have bills to pay every year. They overcome "alternate" bearing tendencies by managing the crop load. They also manage fertility and soil moisture to ensure moderate annual shoot extension and a high-but-balanced level of Nitrogen and carbohydrates.

The cycle is often synchronized by a synchronizing event like a late freeze or a serious drought.

But WHY?

What advantage might a species gain by having most individuals having one (or several) years of no seed production followed by a bumper crop? Specimens of synchronized bearing and annual bearing tendencies both exist within a given species. Under conditions that strongly favor annual bearing one would expect synchronized bearing individuals to be rare. There must be compelling reasons that favor individuals with synchronize bearing characteristics.

The leading theory for synchronized bearing is predator avoidance. Trees cannot flee weevils. They are rooted to the ground. The effect of several years of not bearing is to starve out those insects that would otherwise come to an equlibrium with the food base if the trees were to bear annually. The greatly diminished population of pests cannot find and infest all of the nuts, or fruit, of those infrequent, massive crops.

Some pests can infest many different species. The different species sharing a give habitat often follow their own synchronized schedule. So how does the "predator avoidance" theory mesh with the messiness of multiple species?

They mesh rather elegantly, actually. Each plant species typically has a different time window of maximum vulnerability. A peak crop of a plant species with a late window will drag the timing of (i.e., genetically shift) the pest to peak later in the season. Consequently, the peak pest pressure will miss the window of maximum vulnerability for earlier species. In a similar way a peak crop of a very early species will shift the peak pest pressure to earlier in the season thereby clearing the way for later species.

Is there any evidence?

There is anecdotal evidence that some of the selections most notable for annual bearing (McDaniel's burenglish oak) also appear to be one of the most susceptible to weevils.